The nucleus of the solitary tract (NST) receives peripheral input primarily from the facial (VII), glossopharyngeal (IX) and vagus (X) nerves. Primary sensory afferents ultimately reach the NST via the solitary tract. The rostral pole or gustatory recipient zone of the NST receives the special visceral afferents of taste arising mainly from the anterior tongue and traveling in the chorda tympani or sensory component of VII. The objective of this proposal is to investigate the intrinsic morphological organization of the gustatory NST using light and electron miscroscopic methods. The patterns of terminations of primary gustatory afferents are analyzed in relation to the morphologically distinct classes of neurons and processes which constitute the gustatory NST and the issue of specialized modes of synaptic contact on particular classes of neurons are addressed. The terminations of the primary gustatory afferents are compared to those of centrifugal afferents arising from the insular cortex and brainstem in order to examine the levels of central influences on gustation. The synaptic interactions among the classes of neurons in the gustatory NST are studied in regards to the existence of inhibitory local control neurons and their potential influence on output neurons and on activity leaving the gustatory NST. This proposal seeks to elucidate the morphological substrates of the input-output circuitry of the gustatory NST and to clarify the basic anatomical principles governing the processing of gustatory information. These studies use various stains, and coordinated HRP, Golgi and combined Golgi-EM methods to define the architecture of the gustatory NST, the axonal profiles of the solitary tract and the distributions, sizes and features of the neurons of the gustatory NST at the light microscopic and ultrastructural levels. This proposal represents an initial inquiry into the organization of the NST in relation to the special sense of taste and the general visceral afferents, and in comparison to the olfactory system.